I posted this over on the Gigabyte forums too, but I thought I'd check here for some input. I've had my motherboard for a couple of months now. I have an i5-3570k in it, and it's overclocked to 4.3 GHz currently. I've also got a nVidia GTX 660 for video, hooked up through HDMI to my TV. Lately, I've been experiencing a few interesting crashes.

Most recently, last night I left my computer on to upload a torrent. About 6 hours into the night, I woke up to a terrible buzzing noise coming from my speakers, like the sound output is locking up or something. I checked the error code on the motherboard, and noticed A0 - the manual lists "IDE initialization started". I don't have any IDE devices connected to the motherboard. In fact, I wasn't aware that there was even an IDE header on the board.

I've seen the same symptoms a couple of times while gaming, too. If I'm fullscreen for a long period of time, 3 or 4 hours maybe, the computer locks and I get the same buzzing/locked sound output. No blue screen, no restart, it just hangs until I physically reboot. Since I have to manually restart, I don't really have any dump info or other helpful information to post, either.

I know these issues aren't thermal; my idle temps are around 30C, and load temps while gaming sit at about 50-60C. I thought it might be a CPU voltage issue with the overclock, but it was 48 hours stable under Prime95, and now that I'm seeing the same issue at load and idle, I'm not so sure.

Go back to default Bios settings (remove overclock) and see if the problem is still there.
Have you tested your memory using memtest?
Is the 840 connected to a native Intel SATA port? try a different port/cable.

I have not experienced this issue on my current setup, but I did experience something similar on a 775 socket build I had previously. The computer will lock up all of a sudden and I get buzzing annoying noise from the speakers. I backed out my overclock and that fixed it for me. Not sure if this the same problem, but just to eliminate any overclock issue, just back it out and test it for a while. Really cannot assume your overclock is stable even with 48 hours prime test. From my understanding, issue such as this happens due to Vdroop, etc. So, perhaps once you make sure your problem does not occur at stock settings, you can then re-check your overclock setting.

If no issues arise when stock, it just means your oc wasn't stable. No faulty mobo or anything, which is good news for you.

Definitely. I'm not to the point where I'm starting to consider bad parts, since its such a weird intermittent issue. I'd love it if I could get some more detailed crash info, but that's the way the ball bounces I guess.

Once you determine that your system is stable at stock clocks, there are folks here that can get you to a stable OC (assuming your cpu or another component is not dud). I personally used the following guide:

I used the DVID method and got stable 4.5 Ghz overclock at 1.25V. I have the power saving options turned on and made sure my LLC is at a value recommended by the guide. Perhaps your LLC is not set right causing you a vdroop (when system comes in and out of power saving) which makes it unstable?